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MOND, a Paper and a Question



 
 
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Old April 1st 04, 08:58 PM
Tom Kirke
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Default MOND, a Paper and a Question

arXiv.org just posted a paper on MOND, here is the abstract:
================================================== ============
astro-ph/0403694 [abs, ps, pdf, other] :

Title: Relativistic gravitation theory for the MOND paradigm
Authors: Jacob D. Bekenstein
Comments: ReVTeX and 3 eps figures; 33 pages; submitted to Physical
Review D

The modified newtonian dynamics (MOND) paradigm of Milgrom can boast of a
number
of successful predictions regarding galactic dynamics; these are made
without the
assumption that dark matter plays a significant role. MOND requires
gravitation to
depart from Newtonian theory in the extragalactic regime where dynamical
accelerations
are small. So far relativistic gravitation theories proposed to underpin
MOND have
either clashed with the post-Newtonian tests of general relativity, or
failed to
provide significant gravitational lensing, or violated hallowed principles
by exhibiting
superluminal scalar waves or an a priori vector field. We develop a
relativistic MOND
inspired theory which resolves these problems. In it gravitation is
mediated by metric,
a scalar field and a 4-vector field, all three dynamical. For a simple
choice of its free
function, the theory has a Newtonian limit for nonrelativistic dynamics
with significant
acceleration, but a MOND limit when accelerations are small. We calculate
the beta and
gamma PPN coefficients showing them to agree with solar system
measurements. The gravitational
light deflection by nonrelativistic systems is governed by the same
potential responsible
for dynamics of particles. Consequently, the new theory predicts
gravitational lensing by
extragalactic structures that cannot be distinguished from that predicted
within the dark
matter paradigm by general relativity. Cosmological models based on the
theory are quite
similar to those based on general relativity; they predict slow evolution
of the scalar
field. For a range of initial conditions, this last result makes it easy
to rule out
superluminal propagation of metric, scalar and vector waves.
================================================== ===================

And a question.

We now know of galaxies that do not exhibit the higher rotational
velocities that are,
presumably, diagnostic of Dark Matter. These galaxies also seem to have
all gas stripped.
This has been intepreted as implying that DM is a gas ( WIMPs rather that
MACHOs ). Doesn't
this contradict the predictions of MOND? The dynamics should be invarient
and not depend
on the enviromental history of the galaxy?

Dark skies,

tom

--
We have discovered a therapy ( NOT a cure )
for the common cold. Play tuba for an hour.
 




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